PICEOCLEIDUS. 139 



remur: length 32-0 



greatest width of upper end (crushed) 9'7 



width of shaft at narrowest 6-0 



„ distal end 16*2 



Tibia : greatest length 6-7 



width 80 



Fibula : greatest length 6-6 



,, width 8"5 



The vertebrge and shoulder-girdle are too much crashed and imperfect to give any 

 measurements of value. 



Genus PICEOCLEIDUS, Andrews. 

 [Ann. Mag. Nat. Hist. [8] vol. iv. (1909) p. 421.] 



Plesiosaurs in which ossification is complete while they are still of very small size. 

 Skull known only from a few fragments, resembling generally the same parts of the 

 skull of TricleidiLS seeleyi. The neck includes upwards of thirty-nine vertebrge, the 

 centra of which are shorter than in Ilurcenosaurus (especially in the anterior region) 

 and longer than in Cry])tocleidus. The ends of the centra are considerably wider than 

 high and are almost fiat, often with a small mammilla in the centre. The single- 

 headed cervical ribs of the anterior part of the neck have a distinct anterior limb 

 (PI. VII. fig. 5, a.p.), which further back in the series may be reduced to a small angular 

 projection on the anterior border. The neural spines on the anterior part of the neck 

 are low and rather wide, but they increase gradually in height till in the hinder region 

 they are both wide and high (Pl.YII. fig. 3). In the shoulder-girdle (PL VII. figs. 2, '2a; 

 text-fig. 70) the clavicular arch consists of a small interclavicle shaped somewhat like 

 an arrow-head and triangular in section ; the clavicles, if present at all, seem to be 

 represented by mere films of bone, adherent to the visceral face of the scapulae. These 

 are of a typically Elasmosaurian type, meeting in the middle line in an extensive suture 

 and extending back to meet the anterior median prolongation of the coracoids. 

 Anteriorly they are separated by a notch for the reception of the interclavicle. The 

 coracoids are comparatively short, posteriorly they are produced backwards into blunt 

 processes, both at their outer and inner angles. The humerus is only slightly expanded 

 distally and articulates with the radius and ulna only. These bones show a tendency 

 to greater elongation than is usual in the family. The pelvis is imperfectly known ; it 

 seems to resemble that of Murcenosaurus rather closely, but the expanded blade of the 

 ischium is relatively longer. 



This genus is distinguished from Cryptocleidus and Tricleidiis by the greater 



t2 



